/*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  
  package io.netty.handler.codec.socksx.v5;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufUtil;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.DecoderException;
  import io.netty.handler.codec.DecoderResult;
  import io.netty.handler.codec.ReplayingDecoder;
  import io.netty.handler.codec.socksx.SocksVersion;
  import io.netty.handler.codec.socksx.v5.Socks5CommandRequestDecoder.State;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.UnstableApi;
  
  import java.util.List;
  
  /**
   * Decodes a single {@link Socks5CommandRequest} from the inbound {@link ByteBuf}s.
   * On successful decode, this decoder will forward the received data to the next handler, so that
   * other handler can remove or replace this decoder later.  On failed decode, this decoder will
   * discard the received data, so that other handler closes the connection later.
   */
  public class Socks5CommandRequestDecoder extends ReplayingDecoder<State> {
  
      @UnstableApi
      public enum State {
          INIT,
          SUCCESS,
          FAILURE
      }
  
      private final Socks5AddressDecoder addressDecoder;
  
      public Socks5CommandRequestDecoder() {
          this(Socks5AddressDecoder.DEFAULT);
      }
  
      public Socks5CommandRequestDecoder(Socks5AddressDecoder addressDecoder) {
          super(State.INIT);
          this.addressDecoder = ObjectUtil.checkNotNull(addressDecoder, "addressDecoder");
      }
  
      @Override
      protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
          try {
              switch (state()) {
              case INIT: {
                  final byte version = in.readByte();
                  if (version != SocksVersion.SOCKS5.byteValue()) {
                      throw new DecoderException(
                              "unsupported version: " + version + " (expected: " + SocksVersion.SOCKS5.byteValue() + ')');
                  }
  
                  final Socks5CommandType type = Socks5CommandType.valueOf(in.readByte());
                  in.skipBytes(1); // RSV
                  final Socks5AddressType dstAddrType = Socks5AddressType.valueOf(in.readByte());
                  final String dstAddr = addressDecoder.decodeAddress(dstAddrType, in);
                  final int dstPort = ByteBufUtil.readUnsignedShortBE(in);
  
                  out.add(new DefaultSocks5CommandRequest(type, dstAddrType, dstAddr, dstPort));
                  checkpoint(State.SUCCESS);
              }
              case SUCCESS: {
                  int readableBytes = actualReadableBytes();
                  if (readableBytes > 0) {
                      out.add(in.readRetainedSlice(readableBytes));
                  }
                  break;
              }
              case FAILURE: {
                  in.skipBytes(actualReadableBytes());
                  break;
              }
              }
          } catch (Exception e) {
              fail(out, e);
          }
      }
  
      private void fail(List<Object> out, Exception cause) {
          if (!(cause instanceof DecoderException)) {
              cause = new DecoderException(cause);
          }
  
         checkpoint(State.FAILURE);
 
         Socks5Message m = new DefaultSocks5CommandRequest(
                 Socks5CommandType.CONNECT, Socks5AddressType.IPv4, "0.0.0.0", 1);
         m.setDecoderResult(DecoderResult.failure(cause));
         out.add(m);
     }
 }